All ram BOP’s must be equipped with a ram lock system that can either be manual operated or hydraulic operated to assure that the ram does not open if the hydraulic closing pressure is lost. If it is a manuel system it should be equipped with extension hand wells.
Wedge Lock (Cameron Iron Works)
The Wedge Lock System (Fig 34) is a hydraulically operated mechanical locking mechanism, thus demanding a separate hydraulic system to be activated and deactivated.
The wedgelock system will lock the rams in their closed position and maintain the rams mechanically closed and locked eventhough the actuating pressure is released.
The hydraulic operating system can be interlocked using sequence valves to ensure that the wedgelock is retracted before pressure is applied to open the rams.
For subsea applications, a pressure balance chamber is connected to the wedgelock housing to eliminate the possibility of the wedgelock becoming unlocked due to hydrostatic seawater pressure.
Poslock (Shaffer)
Shaffer ram BOPs equipped with Poslock (Fig 35) pistons are locked automatically in the closed position each time they are closed. The rams will remain locked in the closed position even if closing pressure is removed. Hydraulic pressure supplied to the
open side of the pistons is required to reopen the rams.
The Poslock System utilises locking segments to achieve the positive mechanical lock. The Poslock System has one set of locking segments, which provides for one unique position locking. When the front packer elastomers on the rams become worn the Poslock System cannot automatically compensate for increased distance between the mating ram packers. The activation of the Poslock System to lock and to unlock the rams will happen as a result of the mechanical design making the system independent from any additional hydraulic activating systems.
Fig. 34
When closing the rams the hydraulic pressure is applied to the closing side of the pistons. The two complete piston assemblies move towards the well centre until they contact each other. When the pistons have reached the fully closed position the locking segments have then reached the position where the larger cylinder liner diameter begins.
The closing hydraulic pressure is also exposed to the locking cone, which is a separate part placed inside the piston. The hydraulic force on the locking cone makes it travel a further distance towards the well centre inside the piston. This additional travel distance forces the locking segments to move radial outwards due to the tapered shoulder on the locking cone. The segments lock the piston in the cylinder liner.
The locking cones maintain the locking segments in position. Springs ensure that the locking cone position is maintained also if the hydraulic closing pressure is removed.
To open the rams again hydraulic opening pressure is supplied to the pistons opening side. Initially the locking cone will travel a short distance inside the piston. This allows the locking segments to retract allowing the piston to open the rams.
UltraLock (Shaffer)
Shaffer ram BOPs that are equipped with the UltraLock (Fig 36) system are locked automatically in the closed position each time the rams are closed. The rams remain locked in the closed position also if the hydraulic closing pressure is removed. Hydraulic opening pressure is required to unlock and re-open the rams.
The locking system is mechanical and consists of spring loaded locking dogs that are engaged against restrained locking rods. Four rods per piston are used with four mating locking dogs. The load is carried simultaneously on a pair of two rods and locking dogs which are placed 180 degrees apart. This allows a greater number of locked positions.
Due to the design no additional hydraulic lines or functions are required for activating and deactivating of the UltraLock.
Hydraulic pressure is applied to the
pistons when closing. The entire piston assembly moves towards the well centre together with the rams. When the rams meet each other the motion becomes restricted. At this stage the hydraulic pressure forces the secondary piston to move an additional distance within the UltraLock piston. This allows the locking segments to move radial outwards. The
radial motion supported by springs engages the locking segments into their respective locking rods.
The rams will be maintained in the locked position even if the hydraulic pressure is lost or removed.
The interlock between the locking rods and the locking dogs is obtained by a mating tooth profile machined into the surface of the locking rods and in the locking dogs.
With wear on the front packer elastomers the further motion of the assembly towards the well centre will make the locking dogs engage at this new position.
The UltraLock adjusts the locking position closer to the well centre along with wear on the front packer elastomers.
When hydraulic pressure is applied to open the rams, the secondary piston responds at first and consequently the locking segments become disengaged. Consequently the UltrLock piston can move unrestricted and open the rams.
UltraLock II (Shaffer)
The Shaffer UltraLock II locking system (Fig 37 & 38) incorporates a mechanical locking mechanism within the piston assembly.
The locking system is independent of hydraulic closing pressure to remain locked. It uses flat tapered locking segments carried by the operating piston, which engages with another stationary and tapered shaft fixed in the operating cylinder. When using SL-D rams, the UltraLock II has hang-off capabilities up to 600,000 pounds at full working pressure.
The system needs no adjustments, no matter the size of the pipe rams. Different size or type ram assemblies can be freely interchanged.
Fig. 37
Only one hydraulic function is required to operate the cylinder’s open/close function and the locking system. The system automatically locks in the closed position each time the piston assembly is closed compensating for front packer wear. Once the operating piston is closed on the pipe, the locks are engaged until opening pressure is applied. Only hydraulic pressure can unlock and reopen the rams.
Multiple Position Locking MPL (Hydril)
Some Hydril ram BOPs are available with automatic Multiple Position ram Locking MPL (fig39 & 40). MPL allows the ram to seal off with optimum seal squeeze effect on every closure. MPL automatically locks and maintain the rams closed with optimum rubber pressure required for seal off on the front packer and upper seal.
Front packer seal wear (on any ram BOP) requires a different ram locking position closer to the well centre to ensure an effective seal off. MPL is designed to automatically adjust to the new seal off position.
A mechanical lock is automatically set each time the ram is closed. Ram closure is accomplished by applying hydraulic pressure to the closing chamber, which moves the ram to a seal off position. The locking system maintains the ram mechanically locked while seal off is retained even after releasing hydraulic closing pressure. The ram is opened only by application of hydraulic opening pressure. This releases the locking system initially and then opens the ram.
Fig. 39
Fig 39 shows the ram maintained closed and sealed off by the MPL. Hydraulic closing pressure has been released. The Hydril ram BOP automatically maintains ram closure and seal off. MPL will maintain the required rubber pressure on the front packer and upper seal to ensure a seal off up to the BOP Rated Working Pressure. MPL will maintain the seal off without closing pressure and with opening forces created by hanging the drill string on the ram.
A unidirectional clutch mechanism and a lock nut control locking and unlocking of the MPL. The unidirectional clutch mechanism maintains the nut and ram in a locked position until the clutch is disengaged by application of opening hydraulic pressure.
Hydraulic opening pressure disengages the clutch plates to permit the lock nut to rotate freely and the ram to open.
The travel of the piston and the threaded tail rod during closing or opening the ram causes the lock to rotate. The fast lead six-path helical thread rotates the nut three turns per foot of travel.